1. Field of the Invention
This invention relates generally to the separation of non-miscible liquids and to compositions useful in that separation.
More specifically, this invention relates to the separation of hydrocarbons, colorinated hydrocarbons, and similar liquids from water.
In one preferred embodiment, this invention is directed to the removal and recovery of spilled hydrocarbons from the surface of a body of water.
2. Description of the Related Art
The use of high molecular weight polymers to aid in the control of oil spills and to allow recovery of the oil has been disclosed in commonly assigned U.S. Pat. No. 4,420,400. That patent describes a process for bodying a liquid hydrocarbon by dissolving sufficient polymer therein to substantially increase its effective viscosity and thereby converting the liquid to a semi-solid gel or to a rubbery solid. Successful practice of the disclosed process requires that the polymer be cryogenically comminuted and applied to the hydrocarbon in association with a cryogenic refrigerant.
Another commonly assigned patent, U.S. Pat. No. 4,340,076 to Weitzen, discloses a cryogenic process for dissolving polymers.
Weitzen found that high molecular weight polymers would very rapidly, almost instantaneously, dissolve in solvents for those polymers if the polymer was comminuted at cryogenic temperatures and the resulting polymer particles were introduced into the solvent without allowing them to warm. Polymer concentrations in the solution ranging from a few parts per million to 15% or more could readily be obtained. Essentially no polymer degradation, as indicated by a reduction in the molecular weight of the polymer, occurs during the dissolution.
It is also common to prepare extremely dilute solutions--usually between about one and one hundred ppm--of high molecular weight polymers in solvents such as hydrocarbons. Such solutions display unusual and useful flow characteristics.
In particular, certain linear polymers, such as the high molecular weight alpha-mono olefinic polymers are noted for their effectiveness as drag reducing agents and as anti-misting agents. A drag reducing agent is a polymer which, when dissolved in a solvent, substantially reduces the friction loss during turbulent flow of the solution. An anti-misting agent is a polymer which, when dissolved in fuel, serves to significantly increase medium droplet size and reduce flammability of fuel sprays caused by high velocity wind shear such as occurs during an aircraft crash landing.
However, those high molecular weight polymers are notoriously difficult to dissolve without degradation and without significant reduction in molecular weight. It is not uncommon for such polymers to require several weeks of gentle agitation in a solvent to dissolve completely. Even when the concentration of polymer in such solutions is limited to a few percent at best because of the rapid increase in viscosity with increasing polymer concentration.
Among the approaches taken in the prior art to the problem of preparing polymer solutions is that described in British Patent No. 1,452,146. That patent describes a method and apparatus for dissolving high molecular weight polymers on a large scale in solvents such as crude oil without significant polymer degradation. Patentees use a dissolving vessel having at least two compartments formed by a partition with provision for liquid communication between the compartments at the top and bottom of the partition. Polymer is introduced into moving or agitated solvent within the vessel to form a slurry. Agitation is accomplished by sparging gas into the bottom of one of the compartments to disperse the polymer particle throughout the solvent so as to prevent the polymer particles from agglomerating and to speed the dissolution process. Exemplary data set out in the patent shows the dissolving of crumb or cut polyisoprene of about 8 million molecular weight in crude oil at 32.degree. to form a solution of about 0.92% in about 120 to 160 hours. The molecular weight of the rubber was reduced by about 10% during the dissolution. The maximum concentration of polymer obtainable is determined by the viscosity of the final solution and, for high molecular weight polymers, maximum concentration ranges from about 0.5 to 2% by weight. The solution of polymer obtained is then metered into a flowing stream of crude oil to provide drag reducing effects.
Yet another approach to the preparation of dilute solutions of high molecular weight polymers is set out in the Mack patent, U.S. Pat. No. 4,433,123. Mack polymerizes an olefin in a suitable solvent to obtain a relatively concentrated polymer solution. The entire mixture, containing polyolefin, solvent and catalyst particles, is used without separation to make up dilute solutions of the polymer in crude oil or other hydrocarbons.
This last approach, to use the entire reaction mixture of a polymerization process, is presently most favored from a commercial standpoint because of the great difficulties experienced in dissolving solid polymers without degradation. Drag reducing agents in field use today typically comprise a high molecular weight polymer dissolved in the polymerization solvent, which may be hexane or heptane, at a concentration ranging from a low of 2 to 3% to a maximum of 11 to 12%. These polymer solutions at typical commercial concentrations are thick, viscous liquids which are highly thixotropic and are also highly viscoelastic. They are commonly transported and stored in containers which can be pressurized with an inert gas to pressures of 30 to 70 psig in order to discharge the liquid from the container. Generally speaking, the lower the polymer concentration, the more rapidly and easily it will dissolve in crude oil or other liquids. The upper limit to polymer concentration is set by practical considerations including the need for an acceptably short dissolving time and the need to handle the concentrated polymer solution using readily available and reasonably priced equipment.
It has also been suggested in U.S. Pat. No. 4,584,244 to prepare polymers in the form of agglomeration resistant, free-flowing powders by coating the polymer particles with alumina. This was accomplished by freezing a mixture of the polymer and alumina and thereafter grinding the frozen mixture.
As may readily be appreciated, these prior art approaches to the task of dissolving a high molecular weight polymer in an oil layer floating on water, as is required to practice certain embodiments of this invention, is unwieldly or impossible to accomplish using methods known in the art. Dissolving a solid polymer directly into a crude oil or other solvent liquid is very time consuming and usually results in significant degradation of the polymer. The dissolving process of the Weitzen patent, U.S. Pat. No. 4,340,076 requires a source of liquid nitrogen for its operation as does U.S. Pat. No. 4,420,400. The present commercial approach to the preparation of dilute polymer solutions, which utilizes the entire polymerization mixture, is unwieldy because the polymer solution must be transported and stored in pressure vessels such as those used to ship and store propane and butane. It also incurs a substantial financial penalty for transportation because little more than 10% of the mixture is polymer. Further, the polymerization mixture is a very difficult liquid to handle. It is highly viscoelastic and extremely thixotropic, the breakout viscosity being as high as several million centipoise.
It is evident that the prior art approaches to dissolving polymers present practical and economical difficulties when the solvent is widely dispersed as, for example, is a layer of oil on water.